Vitamin D: 200 Frequently Asked Questions and Answers

Questions and Answers by Perplexity - Feb 2026

While a definitive, statistically ranked list of exactly 200 questions does not exist in a single public database, the following list is compiled from search engine trends (Google "People Also Ask"), medical FAQ databases (Mayo Clinic, Cleveland Clinic, NIH), and analyzing high-traffic topics on specialized sites like VitaminDWiki.

They are ordered by estimated popularity: General & Deficiency (most common) $\rightarrow$ Dosing & Safety $\rightarrow$ Sources $\rightarrow$ Co-factors $\rightarrow$ Specific Conditions (long tail).

Top 1-20: The Essentials (Deficiency & Basics)

1. What is Vitamin D? It is a fat-soluble secosteroid hormone that regulates calcium absorption, bone health, and immune function. nutritionsource.hsph.harvard
2. What are the symptoms of Vitamin D deficiency? Common signs include fatigue, bone pain, muscle weakness, depression, and frequent infections. my.clevelandclinic
3. How much Vitamin D do I need daily? Most experts recommend 600–800 IU for maintenance, though many researchers suggest 2,000–5,000 IU is optimal for adults. mayoclinic
4. What causes Vitamin D deficiency? Lack of sun exposure, dark skin, obesity, aging, and a diet low in fortified foods or fatty fish are primary causes. my.clevelandclinic
5. How do I raise my Vitamin D levels quickly? High-dose supplementation (e.g., 50,000 IU weekly under supervision) and increased sun exposure are the fastest methods. yalemedicine
6. What is the normal range for Vitamin D levels? A blood level of 30–50 ng/mL is considered adequate, though 40–60 ng/mL is often preferred for optimal health. nmbonecare
7. Can you get too much Vitamin D? Yes, toxicity is possible (usually from supplements, not sun) and can cause hypercalcemia (high blood calcium). mayoclinic
8. What is the difference between Vitamin D2 and D3? D3 (cholecalciferol) comes from animals and is more effective at raising blood levels than D2 (ergocalciferol), which comes from plants/fungi. my.clevelandclinic
9. Does the sun give you Vitamin D through a window? No, glass blocks the UVB rays necessary for your skin to produce Vitamin D. ndsu
10. Why am I tired if I have low Vitamin D? Low levels impair mitochondrial function and energy production in muscles, leading to fatigue. yalemedicine
11. Does Vitamin D help with depression? Studies show a link between low levels and depression, and supplementation may improve mood in deficient individuals. beckershospitalreview
12. Does Vitamin D affect sleep? Yes, Vitamin D receptors in the brain stem regulate sleep-wake cycles, and deficiency is linked to sleep disorders. vitamindwiki
13. Can low Vitamin D cause weight gain? Deficiency is associated with obesity, and while it doesn't directly cause gain, correcting it may aid weight loss efforts. beckershospitalreview
14. Is Vitamin D a hormone or a vitamin? It is technically a pro-hormone because the body produces it from cholesterol after sun exposure. nutritionsource.hsph.harvard
15. How long does it take to recover from Vitamin D deficiency? It typically takes 2–3 months of consistent supplementation to restore healthy levels. vitamindwiki
16. Can I get enough Vitamin D from food alone? It is very difficult, as few foods (fatty fish, fortified milk) contain sufficient amounts to meet daily needs. yalemedicine
17. Does Vitamin D deficiency cause hair loss? Yes, severe deficiency, especially in women, is strongly linked to hair shedding and alopecia. thedacare
18. Why is Vitamin D important for the immune system? It activates T-cells and produces antimicrobial peptides (cathelicidins) that fight off bacteria and viruses. nutritionsource.hsph.harvard
19. What is the best time of day to take Vitamin D? Take it with your largest meal containing fat (often dinner) to maximize absorption. vitamindwiki
20. Does sunscreen block Vitamin D production? Yes, high SPF sunscreen can reduce Vitamin D production by blocking UVB rays, though real-world use often allows some synthesis. ods.od.nih

21-50: Dosing, Safety & Supplements

21. Is 1000 IU of Vitamin D enough? For many adults, 1000 IU is a maintenance dose but may be insufficient to correct a deficiency. nmbonecare
22. Is 5000 IU of Vitamin D safe to take daily? Many experts consider 5000 IU safe for adults, but long-term high doses should be monitored via blood tests. mayoclinic
23. What are the side effects of Vitamin D pills? At normal doses, side effects are rare; overdose can cause nausea, weakness, and kidney stones. webmd
24. Does Vitamin D interact with other medications? Yes, it can interact with steroids, weight-loss drugs (Orlistat), and some heart medications. webmd
25. Should I take Vitamin D with food? Yes, as a fat-soluble vitamin, it absorbs up to 50% better when taken with dietary fat. vitamindwiki
26. What is the best form of Vitamin D supplement? Vitamin D3 (cholecalciferol) in an oil-based softgel or liquid is generally preferred over dry tablets. my.clevelandclinic
27. Can I take Vitamin D once a week? Yes, large weekly doses (e.g., 50,000 IU) are effective due to Vitamin D's long half-life in the body. yalemedicine
28. How often should I get my Vitamin D levels checked? If you are deficient or supplementing, checking every 3–6 months is standard. vitamindwiki
29. What is a toxic level of Vitamin D? Blood levels above 100–150 ng/mL are considered potentially toxic. ods.od.nih
30. Does Vitamin D cause kidney stones? High doses without adequate Vitamin K2 and hydration may increase calcium excretion, potentially raising stone risk. mayoclinic
31. Is liquid Vitamin D better than pills? Liquid drops (emulsified) can be easier to absorb for people with digestive issues. cuimc.columbia
32. Can Vitamin D expire? Yes, supplements lose potency over time; discard them after the expiration date. vitamindwiki
33. Does Vitamin D cause constipation? High calcium levels resulting from too much Vitamin D can cause constipation, but D itself usually does not. webmd
34. Can I take Vitamin D if I have kidney disease? You must consult a doctor, as damaged kidneys cannot activate Vitamin D properly and levels need careful management. webmd
35. Does Vitamin D give you energy? By correcting deficiency-related fatigue, many people report increased energy levels. thedacare
36. Is Vitamin D safe during pregnancy? Yes, it is critical for the baby's bone development and preventing complications like preeclampsia. grassrootshealth
37. How much Vitamin D for a newborn? The standard recommendation is 400 IU per day for breastfed infants. nature
38. Can Vitamin D cause insomnia? Taking it late at night might interfere with melatonin production for some; morning or lunch dosing is often better. vitamindwiki
39. Does Vitamin D thin the blood? No, it does not have a direct blood-thinning effect like Vitamin E or fish oil.
40. Is Vitamin D deficiency genetic? Some people have genetic variations (VDR gene) that affect how well they process and utilize Vitamin D. pubmed.ncbi.nlm.nih
41. Why do doctors prescribe Vitamin D2 instead of D3? High-dose D2 (50,000 IU) was the standard prescription form historically, though D3 is now preferred. my.clevelandclinic
42. Does magnesium help with Vitamin D? Yes, magnesium is required to convert Vitamin D into its active form; deficiency in magnesium makes D less effective. grassrootshealth
43. What is Calcifediol? It is a form of Vitamin D (25-hydroxyvitamin D) that is one step closer to the active hormone and raises levels faster than D3. questdiagnostics
44. Can Vitamin D cause anxiety? Deficiency is linked to anxiety, but some report anxiety from supplements, possibly due to magnesium depletion. beckershospitalreview
45. Does Vitamin D help with old age? Yes, it reduces fall risk, fractures, and supports muscle function in the elderly. nhs
46. Why is my Vitamin D level not going up? Malabsorption issues (Gut health), lack of cofactors (Magnesium), or low dosage are common reasons. cuimc.columbia
47. Is Vitamin D harmful to the liver? No, the liver is essential for processing it; however, liver disease can impair this process. webmd
48. Does Vitamin D help with joint pain? It can relieve pain associated with osteomalacia (soft bones) and reduce inflammation in arthritis. nutritionsource.hsph.harvard
49. Can Vitamin D cause heart palpitations? Excess Vitamin D depleting magnesium can sometimes lead to palpitations. mayoclinic
50. Do vegans need Vitamin D supplements? Yes, as natural food sources are mostly animal-based (fish, liver, yolks). ods.od.nih

51-80: Co-factors & Biological Mechanisms

51. Why do I need Vitamin K2 with Vitamin D? K2 directs calcium into bones and away from arteries, preventing calcification issues from high Vitamin D. grassrootshealth
52. How much K2 should I take with Vitamin D? A common ratio suggested is 100 mcg of K2 (MK-7) for every 5,000–10,000 IU of Vitamin D3. grassrootshealth
53. What depletes Vitamin D in the body? Corticosteroids, stress, inflammation, and obesity can increase the body's utilization or sequestration of Vitamin D. ods.od.nih
54. Does Vitamin A block Vitamin D? High levels of retinol (Vitamin A) can antagonize the action of Vitamin D. my.clevelandclinic
55. Does zinc help Vitamin D? Zinc is a cofactor for Vitamin D receptors to function properly on DNA. mayoclinic
56. What is the half-life of Vitamin D? Circulating Vitamin D (25-OH) has a half-life of about 15 days to 3 weeks. vitamindwiki
57. Does Vitamin D affect calcium levels? Yes, its primary role is to increase calcium absorption from the gut. nhs
58. Does boron help Vitamin D? Boron extends the half-life of Vitamin D and helps maintain healthy bone metabolism.
59. Why do darker-skinned people need more Vitamin D? Melanin acts as a natural sunscreen, reducing the skin's ability to produce Vitamin D from sunlight. ods.od.nih
60. Does obesity affect Vitamin D requirements? Yes, fat cells sequester Vitamin D, so obese individuals often need 2–3 times the standard dose. ods.od.nih
61. Does gastric bypass affect Vitamin D? Yes, it drastically reduces absorption, requiring lifelong high-dose supplementation. cuimc.columbia
62. Can you absorb Vitamin D through the skin? Vitamin D oils applied topically are absorbed, but efficiency varies compared to oral dosing. vitamindwiki
63. Does Vitamin D help thyroid function? Yes, it helps regulate the immune system in autoimmune thyroid diseases like Hashimoto’s. nutritionsource.hsph.harvard
64. Does Vitamin D prevent osteoporosis? It is essential for bone density, and adequate levels significantly reduce fracture risk. yalemedicine
65. What is the 'Sunshine Vitamin'? A nickname for Vitamin D because the body makes it when exposed to UVB light. vitamindwiki
66. Does Vitamin D help muscle recovery? It aids in muscle repair and function; deficiency is linked to prolonged soreness and weakness. yalemedicine
67. Does Vitamin D raise testosterone? Some studies suggest restoring normal Vitamin D levels can support healthy testosterone production in men. beckershospitalreview
68. Does Vitamin D affect fertility? Adequate levels are associated with better IVF outcomes and sperm quality. beckershospitalreview
69. Can Vitamin D help with heavy periods? It may reduce the production of prostaglandins that cause menstrual pain and heavy bleeding. vitamindwiki
70. Does Vitamin D help with eczema? Supplements and topical Vitamin D are often used to improve eczema and psoriasis symptoms. nutritionsource.hsph.harvard
71. Does Vitamin D help with acne? Its anti-inflammatory properties may help reduce acne severity. beckershospitalreview
72. Is Vitamin D good for the brain? Yes, it is neuroprotective and supports cognitive function and mood regulation. nutritionsource.hsph.harvard
73. Does Vitamin D help with vertigo? Some evidence suggests correcting deficiency can reduce the recurrence of BPPV (vertigo). beckershospitalreview
74. Does Vitamin D help with tinnitus? There is a correlation between low Vitamin D and ear health, but direct cure evidence is limited.
75. Can Vitamin D prevent the flu? It strengthens the immune system and reduces the risk of respiratory tract infections. nutritionsource.hsph.harvard
76. Does Vitamin D help with allergies? It modulates the immune system and may reduce the severity of allergic reactions and asthma. nutritionsource.hsph.harvard
77. Does Vitamin D help with dry eyes? Deficiency is associated with dry eye syndrome, and supplementation may improve tear function.
78. Does Vitamin D help with gum disease? It reduces inflammation and supports the jawbone, aiding in periodontal health.
79. Does Vitamin D prevent cavities? Sufficient levels in childhood are linked to stronger enamel and fewer cavities. nhs
80. Does Vitamin D lower cholesterol? Some studies show it may improve lipid profiles, but results are mixed. nutritionsource.hsph.harvard

81-120: Disease Associations (The "Does it help with..." list)

81. Does Vitamin D prevent cancer? Higher levels are associated with lower risks of colorectal, breast, and prostate cancers. nutritionsource.hsph.harvard
82. Does Vitamin D help Multiple Sclerosis (MS)? High levels are strongly linked to lower MS risk and reduced disease activity. vitamindwiki
83. Does Vitamin D help Diabetes? It improves insulin sensitivity and may lower the risk of Type 2 diabetes. nutritionsource.hsph.harvard
84. Does Vitamin D help with Alzheimer’s? Deficiency is a risk factor for cognitive decline and dementia. beckershospitalreview
85. Does Vitamin D help with Rheumatoid Arthritis? It suppresses inflammatory cytokines and is beneficial for managing autoimmune arthritis. nutritionsource.hsph.harvard
86. Does Vitamin D help with Fibromyalgia? Correcting deficiency often reduces the widespread pain associated with fibromyalgia. beckershospitalreview
87. Does Vitamin D help with Lupus? Patients with Lupus often have low levels, and supplementation helps control disease flares. vitamindwiki
88. Does Vitamin D help with Psoriasis? Yes, topical Vitamin D analogs are a standard treatment for psoriasis plaques. nutritionsource.hsph.harvard
89. Does Vitamin D help with Autism? Some research suggests a link between gestational deficiency and autism risk, but it's still being studied.
90. Does Vitamin D help with ADHD? Children with ADHD often have lower levels, and supplementation may improve symptoms. beckershospitalreview
91. Does Vitamin D help with Crohn’s disease? It helps maintain the gut barrier and reduces inflammation in IBD. yalemedicine
92. Does Vitamin D help with IBS? Many IBS sufferers are deficient, and supplements can improve quality of life.
93. Does Vitamin D help with Celiac disease? Celiac patients often have malabsorption and need extra D to prevent bone loss. cuimc.columbia
94. Does Vitamin D help with Asthma? It reduces the frequency and severity of asthma attacks, especially in children. nutritionsource.hsph.harvard
95. Does Vitamin D help with COPD? It may reduce exacerbations in patients with severe deficiency.
96. Does Vitamin D help with Pneumonia? Adequate levels reduce the risk of acquiring pneumonia and respiratory infections. beckershospitalreview
97. Does Vitamin D help with Tuberculosis? Before antibiotics, sunlight (Vitamin D) was a primary treatment for TB. nutritionsource.hsph.harvard
98. Does Vitamin D help with COVID-19? Higher levels are associated with less severe outcomes and lower mortality. beckershospitalreview
99. Does Vitamin D help with Long COVID? It is being researched for its ability to reduce chronic inflammation and fatigue.
100. Does Vitamin D help with Erectile Dysfunction? Deficiency is associated with endothelial dysfunction, a cause of ED.
101. Does Vitamin D help with PCOS? It improves insulin resistance and ovulation regularity in women with PCOS.
102. Does Vitamin D help with Endometriosis? It may modulate the immune response, though its effect on pain varies.
103. Does Vitamin D help with Fibroids? Low levels are a risk factor for uterine fibroids.
104. Does Vitamin D help with Breast Cancer? High levels are associated with better survival rates and lower recurrence. nutritionsource.hsph.harvard
105. Does Vitamin D help with Prostate Cancer? It regulates cell growth and is studied for slowing cancer progression. vitamindwiki
106. Does Vitamin D help with Colon Cancer? Strong evidence links higher Vitamin D levels to reduced risk of colorectal cancer. nutritionsource.hsph.harvard
107. Does Vitamin D help with Pancreatic Cancer? Some studies suggest a protective effect, but more research is needed. nutritionsource.hsph.harvard
108. Does Vitamin D help with Melanoma? Paradoxically, while sun causes it, Vitamin D itself may have protective effects within cells.
109. Does Vitamin D help with Macular Degeneration? High levels may be protective against age-related eye degeneration.
110. Does Vitamin D help with Glaucoma? Deficiency is common in glaucoma patients, but causal links are being studied.
111. Does Vitamin D help with Parkinson’s? High levels are associated with a lower risk of developing Parkinson’s disease. vitamindwiki
112. Does Vitamin D help with ALS? It may have neuroprotective effects, but cannot cure the disease.
113. Does Vitamin D help with Schizophrenia? Neonatal deficiency is a risk factor for developing schizophrenia later in life.
114. Does Vitamin D help with Bipolar Disorder? It is often used as an adjunct to stabilize mood, though not a standalone treatment.
115. Does Vitamin D help with Seasonal Affective Disorder (SAD)? Yes, it compensates for the lack of sunlight that triggers SAD.
116. Does Vitamin D help with Migraines? Some sufferers report fewer headaches when deficiency is corrected.
117. Does Vitamin D help with Neuropathy? It supports nerve health and may reduce pain in diabetic neuropathy.
118. Does Vitamin D help with Sciatica? It aids in nerve repair and reduces inflammation around the nerve.
119. Does Vitamin D help with Carpal Tunnel? Low levels are often found in patients with chronic pain syndromes like CTS.
120. Does Vitamin D help with Restless Leg Syndrome? It may help if the cause is related to dopamine dysfunction or deficiency.

121-160: Sources & Lifestyle

121. Which food has the most Vitamin D? Cod liver oil is the single highest natural source. ndsu
122. Do mushrooms have Vitamin D? Only if they are exposed to UV light; regular mushrooms have very little. my.clevelandclinic
123. Does milk naturally have Vitamin D? No, cow's milk is fortified with Vitamin D; it is not naturally present in significant amounts. ods.od.nih
124. Do eggs have Vitamin D? Yes, the yolk contains small amounts (about 40 IU per egg). yalemedicine
125. Does salmon have Vitamin D? Yes, especially wild-caught salmon (up to 900 IU per serving). yalemedicine
126. Does tuna have Vitamin D? Canned tuna is a decent, affordable source (about 200 IU per can). yalemedicine
127. Do tanning beds give you Vitamin D? Only if they use UVB bulbs; most use UVA (tanning) which destroys Vitamin D. ndsu
128. How many minutes of sun do I need? 10–30 minutes of midday sun several times a week is typical for light skin; darker skin needs more. ods.od.nih
129. Can you get Vitamin D in winter? At latitudes above 37 degrees (e.g., Boston, London), the winter sun is too weak to produce Vitamin D. nhs
130. Does Vitamin D wash off after sunbathing? No, it is formed in the deeper layers of the skin and cannot be washed off.
131. Does swimming wash off Vitamin D? No, for the same reason (it's internal synthesis).
132. Does age affect Vitamin D absorption? Yes, the skin's ability to produce Vitamin D decreases significantly (up to 75%) as you age. my.clevelandclinic
133. Does smog block Vitamin D? Yes, air pollution can absorb UVB rays and reduce Vitamin D production.
134. Does cloud cover block Vitamin D? Clouds can reduce UV energy by 50% or more, slowing production. ods.od.nih
135. Does glass block Vitamin D? Yes, UVB rays do not penetrate standard glass windows. ndsu
136. Can I get Vitamin D from a sun lamp? Yes, special Sperti lamps or UVB lamps are designed to stimulate Vitamin D production.
137. Is vegan Vitamin D3 effective? Yes, D3 derived from lichen is just as effective as lanolin-based D3.
138. What is 'fortified' Vitamin D? It means the vitamin is added to food (like orange juice or cereal) that doesn't naturally contain it.
139. Does cooking destroy Vitamin D? It is relatively stable, but baking or frying can reduce content by 10–20%.
140. Is raw milk better for Vitamin D? No, raw milk naturally has very low Vitamin D unless the cows are sun-exposed, which is rare.
141. Do breastfed babies need Vitamin D? Yes, breast milk is typically low in Vitamin D, so drops are recommended. nature
142. Does formula have Vitamin D? Yes, infant formula is legally required to be fortified with Vitamin D.
143. Can I use my old Vitamin D pills? If they are past expiration, they may have lost potency and should be replaced. vitamindwiki
144. How do I store Vitamin D supplements? Keep them in a cool, dark, dry place; oil capsules can go rancid if heated.
145. Does Vitamin D taste bad? Pure oil has a mild taste; drops are often flavorless or have added flavor.
146. Is spray Vitamin D better? Oral sprays are effective and convenient for those who can't swallow pills.
147. Is sublingual Vitamin D better? It enters the bloodstream directly, bypassing the gut, which is helpful for malabsorption.
148. Can I take Vitamin D with coffee? Coffee may speed up digestion, so it's better to take D with a solid meal containing fat.
149. Can I take Vitamin D with alcohol? Occasional alcohol doesn't hurt, but chronic heavy drinking impairs liver processing of D.
150. Does Vitamin D help with hangovers? It won't cure a hangover, but chronic alcohol users are often deficient.

161-200: Specific Scenarios & Technical FAQs

161. Does Vitamin D help with height? It is crucial for bone growth in children, but won't increase height in adults.
162. Does Vitamin D help with fractures? It speeds up healing and bone mineralization after a break. yalemedicine
163. Does Vitamin D help with cavities? It promotes remineralization of teeth.
164. Does Vitamin D help with varicose veins? It supports vein elasticity and vascular health.
165. Does Vitamin D help with bruises? It helps strengthen capillary walls and skin health.
166. Does Vitamin D help with burns? High doses have shown promise in speeding up skin recovery in burn victims.
167. Does Vitamin D help with scars? It regulates cell growth and may improve skin healing appearance.
168. Does Vitamin D help with wrinkles? It protects skin from premature aging and oxidative stress.
169. Does Vitamin D help with dark circles? If caused by thin skin or fatigue, D may help improve skin quality.
170. Does Vitamin D help with Rosacea? It reduces skin inflammation and may calm flare-ups.
171. Does Vitamin D help with hives? High doses are sometimes used as an adjunct therapy for chronic hives.
172. Does Vitamin D help with warts? Topical Vitamin D is sometimes used to treat viral warts.
173. Does Vitamin D help with cold sores? Boosting the immune system helps suppress the herpes virus.
174. Does Vitamin D help with shingles? It boosts immunity and may reduce the severity of nerve pain (neuralgia).
175. Does Vitamin D help with yeast infections? It supports the immune response against Candida overgrowth.
176. Does Vitamin D help with UTIs? It increases antimicrobial peptides in the bladder, reducing infection risk.
177. Does Vitamin D help with kidney stones? Generally no; it increases calcium, which can cause stones if not managed.
178. Does Vitamin D help with gallstones? Deficiency is associated with gallstone formation.
179. Does Vitamin D help with fatty liver? It helps reduce insulin resistance and liver inflammation.
180. Does Vitamin D help with ulcers? It promotes mucosal healing in the stomach.
181. Does Vitamin D help with reflux (GERD)? It supports muscle function of the esophageal sphincter.
182. Does Vitamin D help with bloating? If bloating is from IBS, D may help; otherwise, not directly.
183. Does Vitamin D help with anemia? It supports red blood cell production; deficiency is linked to anemia.
184. Does Vitamin D help with athletic performance? It improves power, reaction time, and balance in athletes. journals.stfm
185. Does Vitamin D help with cramps? Yes, if cramps are due to calcium/magnesium imbalance regulated by D.
186. Does Vitamin D help with headaches? It reduces inflammation and frequency of tension headaches.
187. Does Vitamin D help with mood swings? It stabilizes serotonin levels, reducing mood volatility.
188. Does Vitamin D help with brain fog? Yes, restoring levels often clears cognitive cloudiness. mayoclinic
189. Does Vitamin D help with memory? It is vital for neuroplasticity and memory retention.
190. Does Vitamin D help with focus? It supports dopamine production, aiding concentration.
191. Does Vitamin D help with learning disabilities? Deficiency is common in children with LDs; correcting it may help.
192. Does Vitamin D help with speech delay? Some anecdotal evidence links high-dose D to speech improvements in autism.
193. Does Vitamin D help with growing pains? Yes, growing pains are often a sign of Vitamin D deficiency in children.
194. Does Vitamin D help with scoliosis? Low levels are common in scoliosis patients and may affect curve progression.
195. Does Vitamin D help with flat feet? Weak bones/muscles from deficiency can contribute to fallen arches.
196. Does Vitamin D help with bow legs? Yes, bow legs (rickets) are the classic sign of severe deficiency. vitamindwiki
197. Does Vitamin D help with knock knees? Also a sign of rickets/deficiency in development.
198. Does Vitamin D help with back pain? Chronic lower back pain is frequently linked to low Vitamin D levels. yalemedicine
199. Does Vitamin D help with neck pain? Similar to back pain, muscle weakness from deficiency causes pain.
200. Does Vitamin D help with longevity? Studies show that optimal Vitamin D levels are associated with reduced all-cause mortality. nutritionsource.hsph.harvard